In recent years, environmental changes caused by environmental pollution have endangered the ecosystem, and new diseases have been increasing. However, due to developments in medical technology, various diseases have been overcome, and an increased number of people have been enjoying a long lifetime. Nevertheless, on the other hand, the number of patients with diseases which induce an abnormality in brain function, such as Alzheimer's disease, Parkinson's disease, etc., has been increasing. Accordingly, still more development of drugs for recovering brain function has been demanded.
Under such circumstances, many drug manufacturers and chemical manufacturers develop novel drugs.
Such drugs are generally administered into an organism by means of oral administration, application, intravenous injection, intramuscular injection, etc. These administration methods are the same in that an administered drug is circulated through the blood stream in an organism, so as to reach an affected part, and directly acts on the affected part. Further, lead compounds and analogues thereof, which are candidates for a drug that will be commercialized in the future, also directly act on an affected part similarly to conventional drugs.
In the case of a drug which is to be administered into an organism by means of oral administration, intravenous injection, or the like, it is necessary to simulate and verify the pharmacokinetics of the administered drug, the absorption rate of the drug, and the efficiency of the drug for reaching an affected part.
Further, in the case where a drug is orally administered, the administered drug is absorbed through the stomach or the small intestine, and the absorbed drug passes through the liver, and then is circulated through the body by means of the blood stream. However, in many cases, a considerable part of the drug which has reached the liver is removed from the body through excretion or metabolism, and as a result, only a portion of the administered drug is utilized. Furthermore, when a drug is administered into a patient who has damage to any of the stomach, the small intestine, or the liver, especially a patient who has damage to the liver, the type and amount of administrable drugs are sometimes limited.
In the case of a drug for a central nervous system of the brain, the administered drug needs to pass through the blood-brain barrier before reaching the inside of the brain. Thus, some drugs cannot reach the inside of the brain due to their chemical structures. Furthermore, since nerve cells having different characteristics are in a complex arrangement inside the brain, unexpected side effects can be caused by a drug that has reached the inside of the brain. It is very difficult to avoid emergence of such side effects.
In the case where a drug reaches an affected part after having been circulated in the body by means of the blood stream, a long time period elapses from when the drug is administered into the body to when the drug reaches and acts on the affected part.
Even when a drug is directly applied to an affected part so that the drug directly acts on the affected part, it is difficult to avoid the above problems.
On the other hand, it has been known that stimulation of the olfactory mucosa is directly transmitted to brain cells, but it is not necessarily clearly elucidated how the brain cells function in response to the stimulation of the olfactory mucosa.